Does this sound familiar? You turn your RV furnace on, you hear the blower run, but it doesn’t light, and the blower turns off. By far, this is the most common problem that people experience when it comes to the RV furnace not working. Does this mean that you need a new furnace? No, in most instances, this is something that you can troubleshoot and fix yourself.
The following tips are only if your RV furnace blows cold air, fails to light, and turns off.
Why your RV furnace doesn’t light?
First, it’s essential to learn how an RV furnace works in order to understand this problem. The problem you’re experiencing is a safety feature of your RV furnace. When you turn on your RV furnace, it will follow a safety startup process. Once the thermostat registers that the requested temperature is higher than the current temperature, it will engage the RV furnace.
The first step of startup an RV furnace is for the furnace blower to turn on. The blower will typically run for 15-30 seconds before the furnace tries to ignite. This test ensures that the blower exhausts any built-up combustibles in the system before it lights. Once the blower runs for a short period, the furnace will receive the signal to ignite. You should hear a clicking sound for the electric igniter at this stage. This sound indicates a spark is being applied to the propane released into the furnace burn chamber.
If the furnace doesn’t light, the RV furnace will recognize this and turn it off. This safety feature prevents propane from running into the RV furnace without ignition. It’s a critical safety feature and is part of every RV furnace.
Solving this problem can seem complicated. However, while it can signify a bad furnace component, it doesn’t always indicate an expensive repair. So before you call out a mobile RV tech or take it in for servicing, there are a few things that you can try yourself, assuming you’re a little handy and comfortable using some basic hand tools.
Below are some troubleshooting steps to follow:
1. Check the propane
One of the most common problems is actually the simplest to solve. You may simply be out of propane, or your propane tank valve may be closed. If this is the case, your furnace will not receive any propane and will be unable to light. You can check your propane tank levels and make sure the valve is all of the way open.
You can also turn on your stove and make sure that it lights. If you have adequate propane for the stove, you should also have it for the RV furnace. If your stove does light, let it run for a minute or so just to make sure that you’re not simply burning any residual propane in the line. If it stays lit and you’re sure the tanks aren’t empty, move to the next step.
2. Sail Switch
The RV sail switch is a simple switch, like a light switch, that once engaged, sends a signal to the propane valve to open. If the switch doesn’t engage, it won’t send that signal, and therefore, your furnace can’t ignite. Next, the blower fan engages the sail switch. The sail switch isn’t too complicated. It is simply a thin piece of metal that sits within the blower’s body. Once the blower is running, the air produced by the blower will force the switch (the thin piece of metal) closed, therefore completing the circuit.
If the blower can’t depress the switch, it will never engage, and therefore, it won’t trigger the propane valve to open. Without the propane valve open, propane can’t release into the furnace, and it won’t light. A telltale sign of a malfunctioning sail switch is when you turn on the furnace, and you hear the blower start up and run, followed by some clicking of the or ignitor. However, it will turn off because it doesn’t light. It doesn’t ignite because the propane valve never opens. This scenario often indicates that the sail switch is not engaging.
There are a few things that can cause this problem. First, while the sail switch may be bad, this is usually not the case. The most common problem with a sail switch is that a small amount of lint or fur gets into the switch and prevents it from closing correctly. If you have animals in your RV, that’s is a good indicator that this may be the problem.
It’s important to note that it only takes a tiny piece of debris (lint, dust, hair) to cause this problem. You can typically remove the switch and clean the blockage by hand if this is the issue. Cleaning the sail switch is not difficult. If you have outside access to the furnace, this can be a 5-minute task. If not, you may need to remove the furnace to access it. If you need to remove the furnace, you’ll likely need to remove the propane supply line connection to do so. This process isn’t complicated, but you should always be careful when working around propane. Always turn your propane is off if you’re working in or around gas lines or appliances. You should also be comfortable working with propane lines and fittings. You’ll need to connect this back up correctly, or you may create a dangerous situation.
An underperforming blower is the other common problem associated with a sail switch that doesn’t engage. If the blower can’t produce enough airflow, it may not engage the switch. While this can always indicate a bad blower, a more typical scenario is a low battery. The blower may be receiving low voltage causing it to run, but not fast enough. A dying battery can always cause this problem. Therefore, it’s important to ensure that you have an adequately charged battery for your furnace to operate.
3. Limit Switch
Once the sail switch engages, it will send power to the gas valve, telling the system to send propane to the furnace. The gas valve will open and allow propane to enter the furnace. While the gas valve can be a problem, it’s not very common. More common is the limit switch. If the sail witch works and powers the gas valve, but there isn’t ignition, the next step is to check the limit switch. A tell-tale sign of a malfunctioning limit switch is that the blower will run, but you won’t hear any clicking of the ignitor. Instead, the fan will blow cold air and then turn off.
Here’s an overview of the steps for the furnace lighting: The thermostat will tell the furnace to turn on, which will engage the blower. The blower will trigger the sail switch and then send power to the limit switch, telling the furnace that it’s time to light. If the limit switch fails, it won’t trigger the ignitor, and you won’t hear the clicking of the furnace trying to ignite. As a result, the fan will stop, and the furnace won’t light.
If you have a bad limit switch, you’ll most likely need to replace it. It’s not a difficult task, but you will need to order a new switch to fix it. You may have a bad connection, but that isn’t very common.
The final step of DIY troubleshooting for this scenario is the ignitor/electrode. Assuming that the sail switch is working and sends the signal to the limit switch to light, the next step is to create the actual spark (the clicking that you hear) to light the propane. If the sail switch and limit switch are operating correctly, you may have a bad ignitor. These don’t typically fail as often as the sail switch and limit switch, but that’s not to mean it can’t.
When diagnosing the ignitor, the first thing to do is remove it and check for corrosion or a broken metal arm. It’s similar to a spar plug where there is a gap between two pieces of metal. If one of the pieces breaks, it can’t create a spark. Likewise, if the gap is too wide or narrow, it may not be able to spark. The required gap is usually ⅛” of an inch. An excellent way to measure this is to insert a ⅛” drill bit in the gap opening. If it doesn’t fit or there is too much room, you can try adjusting it, being careful not to break the switch.
While these are not the only things that can fail on a furnace, they are some of the more common issues people experience when their furnaces don’t light. If your fan blows but fails to light and then turns off, you may be dealing with one of the above problems. You can try to fix/diagnose yourself if you’re comfortable working on appliances. However, you may want to call an RV tech if this is something outside of your comfort zone. You are working with a propane appliance, and you do not want to create a dangerous situation for you or your family.
It’s also important to note that other problems can cause the above issue. One may be a faulty circuit board (the brains of the furnace). Replacing this can be more complicated and expensive. This repair is probably best left to an RV tech.
Knowing your RV and how it works can give you confidence in heading out on the road. In addition, there is a lot of information available to provide you with the knowledge to diagnose problems and fix them. While this can save you some money, it can also save a camping trip if something goes wrong.
Once you get your RV furnace, check out some of these great tips for lowering your RV propane use.